Micro-needle array comprising a color change indicator

ABSTRACT

The invention relates to a microneedle array and to the use thereof for intradermal delivery, comprising a plurality of microneedles on a carrier, wherein this microneedle array is suitable for penetrating the skin of humans or animals and includes at least one color change indicator.

The invention relates to a microneedle array and to the use thereof forintradermal delivery, comprising a plurality of microneedles on acarrier, wherein this microneedle array is suitable for penetrating theskin of humans or animals and includes at least one color changeindicator.

Microneedle systems and devices in which microneedle arrays are used forthe painless intradermal (or transdermal) administration of substances,and in particular of medicinal drugs, are known from the prior art.

The skin consists of several layers. The outermost layer of the skin,this being the stratum corneum, has known barrier properties to preventforeign substances from penetrating into the body and the body's ownsubstances from exiting the body. The stratum corneum, which is acomplex structure composed of compacted horny cell residues having athickness of approximately 10 to 30 micrometers, forms a watertightmembrane for this purpose to protect the body. This naturalimpermeability of the stratum corneum prevents most pharmaceuticalagents and other substances from being administered through the skin aspart of an intradermal delivery.

As a result, various substances are therefore administered, for example,by generating micropores or cuts in the stratum corneum and feeding ordelivering a medicinal drug into or beneath the stratum corneum. In thisway, it is also possible to administer a number of medicinal drugssubcutaneously or intradermally or intracutaneously, for example.

It remains difficult to establish in the prior art whether a microneedlearray has sufficiently penetrated the skin, and the stratum corneum hasbeen reached or this barrier has been overcome.

In the prior art, WO 2009/081122 A1 describes a monitoring system forthe release of medicinal drugs via microneedles. However, the system isnot capable of verifying a penetration into the stratum corneum sincethe included dye only provides information as to whether a substance,this being a medicinal drug here, has been released from themicroneedles.

Furthermore, WO 2009/081122 A1 does not describes the use of suitablecolor change indicators, in particular pH indicators, in particular inthe pH range between 4 and 8.

DE 10 2014 201 605 A1 describes the problem that sufficient skinpenetration is not possible by means of a microneedle array and proposesfor dyes to be present in microcapsules in a delivery system. However,the disadvantage is that such microcapsules require suitable pressure toburst open, and to allow the dye to emerge. The bursting of themicrocapsules is consequently independent of the actual penetration ofthe skin and requires that a minimum pressure be exerted. Theverification is thus indirect.

Such a dermal penetration indicator is subject to the generalrequirement that unambiguous visualization of a successful physicalpenetration into the stratum corneum or through the stratum corneum intothe layers of the skin beneath (epidermis, dermis) has to take place, bymeans of the released penetration indicator.

The object is therefore to enable reliable verification of a sufficientpenetration depth of the microneedles into the skin, and in particularinto the stratum corneum, wherein a direct and immediate verification ispossible.

The present invention, in particular, takes advantage of the fact thatthe pH value on the skin surface is 4 to 5.5 and, by comparison, the pHvalue of the stratum corneum is 6.5 to 7. Using a pH indicator, it isconsequently possible to generate a visible color change during thepassage from the skin surface into the stratum corneum. Moreover, acolor change can also take place as a function of the surrounding areain the achieved penetration depth, and more particularly taking theintradermal surrounding area (SC, epidermis, dermis) into consideration,even without dependence on a pH value. This is especially helpful whenthis color change is accompanied by the penetration of microneedles intothe skin.

According to the invention, such suitable substances are referred to ascolor change indicators. The term ‘color change’ means that a shift inthe color takes place, including from colorless to not colorless, whichis visible to the naked eye, preferably on the skin surface.

The invention thus relates to such a teaching having the features ofclaim 1, this being a microneedle array for use with intradermaldelivery, comprising a plurality of microneedles on a carrier, whereinthe microneedles include at least one color change indicator. A colorchange, in particular of a pH indicator, particularly advantageouslyindicates a sufficient penetration depth into the stratum corneum.

In another embodiment, the color change indicator can be present in themicroneedles and in the carrier.

The microneedle array can comprise a plurality of microneedles so as tobe able to release a substance via the skin or into the skin of apatient, wherein the microneedle array is placed onto the skin of thepatient. Each of the microneedles of the microneedle array preferablycomprises an elongated shaft having two ends, the one end of the shaftforming the base of the microneedle by way of which the microneedle isattached to the planar carrier or by way of which the microneedle isintegrated into the planar carrier. The end of the shaft locatedopposite the base preferably has a tapered shape so as to enable themicroneedle to penetrate into the skin as easily as possible. A hollowmicroneedle can include at least one passage or channel or at least oneborehole, which extends from the base of the microneedle to the tip ofthe microneedle or approximately to the tip of the microneedle. Thepassages preferably have a round diameter.

The microneedles can be produced from a variety of materials and bemade, for example, of a metal, a ceramic material, a semiconductor, anorganic material, a polymer or a composite, each in particular having asolid or semi-solid or hollow design.

Preferred materials for producing such microneedles are, for example,pharmaceutically acceptable stainless steel, gold, titanium, nickel,iron, tin, chromium, copper, palladium, platinum, alloys of theaforementioned metals, silicon, silicon dioxide, and polymers. Thepolymers can particularly preferably include biodegradable polymers,preferably biocompatible polymers and water-soluble polymers, inparticular of biological or non-biological origin, preferably polymerssuch as alpha-hydroxy acids, such as lactic acid and/or glycolic acid,polylactides, polyglycolides, polylactide-co-glycolides, and copolymerswith polyethylene glycol, polyanhydrides, poly(ortho)esters,polyurethanes, polybutyric acids, polyvaleric acids, andpolylactide-co-caprolactones, polyvinyl pyrrolidone (PVP), glycans,glycosaminoglycans and hyaluronan. The polymers can likewise benon-biodegradable polymers, for example, from the group of thepolycarbonates, polyesters or polyacrylamides. In another embodiment,the microneedles are made of a monocrystalline material, such asmonocrystalline silicon.

The microneedles can comprise a shaft having a round cross-section or anon-round cross-section, for example having a triangular, quadrangularor polygonal cross-section. The shaft can have one passage or multiplepassages, extending from the needle base to the needle tip orapproximately to the needle tip. The microneedles can be designed as(barbed) hooks, wherein one or more of these microneedles comprise oneor more such hooks. Furthermore, the microneedles can be configured in ahelical shape and be rotatably disposed and thereby, when a rotatingmotion is applied, facilitate the penetration into the skin andeffectuate anchoring in the skin (DE 103 53 629 A1), in particular atthe desired penetration depth in the epidermis.

The diameter of a microneedle typically ranges between 1 μm and 500 μm,and preferably between 10 μm and 100 μm. The diameter of a passagetypically ranges between 3 μm and 80 μm and is suitable for preferablyliquid substances, solutions and substance preparations to pass through.The length a microneedle typically ranges between 10 μm and 1,000 μm,and in particular between 100 μm and 500 μm.

The microneedles are attached at the base thereof to a planar carrier orare integrated into a planar carrier. The microneedles are preferablydisposed so as to be situated substantially perpendicularly to thesurface area of the carrier. The microneedles can be arranged regularlyor irregularly. An arrangement of multiple microneedles can comprisemicroneedles having differing cross-sectional shapes, differentlydimensioned diameters and/or differing lengths. The arrangement ofmultiple microneedles can exclusively comprise hollow microneedles. Thearrangement can likewise comprise solid microneedles as well assemi-solid composites, such as solid microneedles interspersed withliquid inclusions.

The microneedle array can comprise a planar carrier, wherein the carrieressentially has a disk-shaped, plate-shaped or film-shaped basic shape.The carrier can have a round, an oval, a triangular, a quadrangular or apolygonal base surface area. The carrier can be produced from a varietyof materials, such as a metal, a ceramic material, a semiconductor, anorganic material, a polymer or a composite. Materials suitable forproducing the carrier can preferably be films or web-shaped materials,for example microporous membranes, preferably made of polyethylene (PE)or polypropylene (PP), or diffusion membranes, preferably made ofethylene-vinyl acetate copolymer (EVA) or polyurethane (PUR). Suitablematerials for producing the carrier can be selected from the groupconsisting of polyesters, such as polyethylene terephthalates (PET),polycarbonates (PC), polyether ketones (PAEK), polyethylene naphthalate(PEN), polybutylene terephthalates (PBT), polyurethanes (PU),polystyrenes (PS), polyamides (PA), polyoxymethylene (POM), polyolefinssuch as polyethylene (PE) and polypropylene (PP),polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyvinylidenechloride (PVDC), polylactate (PLA), and cellulose-based plasticmaterials, such as cellulose hydrate or cellulose acetate. Suitablematerials for producing the carrier can also be selected from the groupof metals, which include aluminum, iron, copper, gold, silver, platinum,alloys of the aforementioned metals, and other pharmaceuticallyacceptable metal foils or metallized films.

The carrier is preferably made of a flexible material, for example aplastic material. A carrier made of a flexible material can betterconform to the surface of the skin and the curvature thereof than acarrier made of a non-flexible material. In this way, better contactbetween the microneedle array and the skin is achieved, therebyimproving the reliability of the microneedle array.

It is now essential for the invention that such a microneedle arraycomprising a color change indicator, and in particular pH indicator, isat least wetted or that preferably a color change indicator, and inparticular a pH indicator, is present.

A pH indicator or a corresponding mixture of pH indicators preferablyexhibits a color shift or color change visible to the naked eye in therange between pH 4 and 8, and in particular 4.5 to 7. Preferred are pHindicators that, when these rest on the skin, display a significantlydifferent color than when these have penetrated the skin, and inparticular reach the stratum corneum as a result of penetration. In thisway, it is possible to achieve a clear color change or color difference,which is clearly visible at the latest after the microneedles have beenremoved.

Suitable pH indicators preferably in the range of pH 4 to 8.5 can be thefollowing, without being limited thereto: nitrazine yellow, bromothymolblue, carminic acid, brazilin, Congo red, neutral red, phenolphthalein,phenolic red, tetrabromophenolphthalein or a mixture thereof.

Likewise, the pH indicators may also be present in the form of mixtures,and corresponding mixed colors can be generated.

In a particularly preferred embodiment, the pH indicator isphysiologically acceptable, such as nitrazine yellow and bromothymolblue.

The color change indicator can further be selected from a compoundselected from chromoionophores or fluoroionophores, wherein the compoundis composed of at least one ionophore covalently bound to at least onemolecule, which is selected from the chromophores and fluorophores. Theionophores are molecules capable of complexing ions.

Chromoionophores or fluoroionophores include shape-imparting groupsthat, in the presence of the intradermal environment (SC, epidermis,dermis), are able to generate a color change, wherein the absorptionspectrum of these molecules can be varied by delocalization of theelectrons, as a result of which the color of the chromoionophores and/orfluoroionophores changes. The chromoionophores and fluoroionophores arecompounds that are composed of one or more ionophoric moleculescovalently bound to at least one molecule, which is selected from thechromophores and fluorophores. A chromophore is a compound that absorbsin the visible range, that is, the compound is colored. Within themeaning of the present application, a fluorophore is a compound thatabsorbs in the UV range and in the visible range, this compound is thuscolored.

According to the invention, suitable chromophores or fluorophores arethose that are selected from the neutral, acidic or basic nitratedbenzene dyes, neutral, acidic or basic (di)azo dyes, including benzidinedyes, quinone dyes, and in particular neutral, acidic or basicanthraquinone dyes, azine dyes, methine dyes, such as neutral, acidic orbasic methines and azomethines, triarylmethane dyes, indoamine dyes,natural dyes, such as carotinoids, terpenoids, flavonoids, porphyrins,fluorescein, rhodamine and coumarins, and direct dyes thereof.

A suitable ionophore is, for example, a salt (alkali salt), such as Na₂,K₂HPO₄, Na, HHCO₃, chelating agent, podands, coronands and cryptands,macrocylic compounds, which are referred to as crown ethers orcoronands, and macrobicyclic compounds, which are referred to ascryptands. Within the meaning of the present application, “podands”shall be understood to mean molecules having an open structure, whichhave ion complexing properties and in which the complexation area is achain containing heteroatoms. These molecules are oligoethers, forexample. Within the meaning of the present application, a “coronand”shall be understood to mean two-dimensional molecules having a closedstructure, which have ion complexing properties. In general, these arehydrocarbon-based monocyclic molecules that contain heteroatoms. Thesemolecules are, for example, macrocyclic polyethers containing thefollowing unit: —(CH2-CH2-Y)n-, where Y denotes a heteroatom selectedfrom O, S, N and P, and n is an integer greater than 2 and preferably inthe range of 4 to 10.

These molecules are, for example, crown ethers, such as 15-crown-5,18-crown-6; benzocrown ethers, such as benzo-15-crown-5,benzo-18-crown-6, dibenzo-15-crown-5, dibenzo-18-crown-6; monoaza crownethers or diaza crown ethers, such as aza-15-crown-5, aza-18-crown-6,diaza-15-crown-5, diaza-18-crown-6. Within the meaning of the presentinvention, “cryptands” shall be understood to mean three-dimensionalmolecules having a closed structure (cages) that have ion complexingproperties. In general, these are hydrocarbon-based bicyclic moleculesthat contain heteroatoms. These molecules are, for example,macrobicyclic polyethers containing the following unit: —(CH2-CH2-Y)n-,where Y denotes a heteroatom selected from O, S, N and P, and n is aninteger greater than 2 and preferably in the range of 2 to 10.

The aforementioned color change indicators can likewise contain anoxidizing agent.

The oxidizing agent is preferably selected from hydrogen peroxide, ureaperoxide, peracid salts, such as perborates and persulfates, peracids,and particularly preferably from enzymes (oxidases, peroxidases).

In another embodiment, the invention can comprise a color changeindicator that detects endogenous enzymes, and in particularperoxidases, which do not form part of the outer layer (epidermis), forexample in the case of peroxides due to the body's natural formation ofhydrogen peroxide from the oxidation of glucose with the aid of glucoseoxidase, such as by means of benzidines, and in particular3,3′,5,5′-tetramethylbenzidine having a specific blue coloration, andphthalazines, such as 5-amino-2,3-dihydrophthalazine-1,4-dione.

Furthermore, ink, and in particular biosensing ink, is a suitable colorchange indicator.

The color change indicator, and in particular pH indicator, can beintegrated or incorporated into the microneedles or into the matrix orformulation of the microarray. Furthermore, the color change indicatorcan be applied onto the microneedles or onto the carrier. However, it ispreferred that the color change indicator, and in particular pHindicator, is an integral part of the microneedle and, for this purpose,can be introduced or incorporated into the microneedles. In particular,the color change indicator can be added, for example to a polymer,during the production of the microneedles.

A color change indicator, and in particular pH indicator, according tothe invention, or a mixture, can be added, for example, during theproduction of such a microneedle array, for example to the matrix. Inanother embodiment, such a color change indicator is an integral part oringredient of a microneedle array or of microneedles, or themicroneedles comprise or consist of at least one color change indicator.

In a particularly preferred embodiment, for example, the tip of at leastone microneedle is wetted with a color change indicator, or a colorchange indicator is included in the tip of at least one microneedle. Forexample, the color change indicator, and in particular pH indicator, canbe integrated or incorporated into the tips of the microneedles. Inparticular, the color change indicator can be added, for example to apolymer, during the production of the tips of the microneedles.

In another preferred embodiment, an active ingredient, and in particulara medicinal drug, can be integrated or incorporated into themicroneedles or into the matrix or formulation of the microarray.Furthermore, at least one active ingredient, and in particular amedicinal drug, can be applied onto the microneedles or onto thecarrier. However, it is preferred that the active ingredient, and inparticular the medicinal drug, is an integral part of the microneedleand, for this purpose, can be introduced or incorporated into themicroneedles, and in particular into the tip of the microneedles. Inparticular, the active ingredient, and in particular the medicinal drug,can be added, for example to a polymer, during the production of themicroneedles. The microneedles comprise or consist of at least onemedicinal drug.

Such medicinal drugs are preferably those defined in EU Directive2001/83/EC (Community code relating to medicinal products for humanuse).

In another specific embodiment, selected microneedles can be providedwith a color change indicator, and in particular pH indicator.

This allows the advantageous application of patterns onto the skin, andin particular patterns such as “plus, cross, star, circle” and otherarbitrary geometric figures, indicating to the naked eye of the patientor the user the successful application or penetration of themicroneedles, also in a visual graphical design.

Moreover, it is preferred that the microneedle array is, or themicroneedles are, made entirely or partially of water-soluble orbiodegradable polymers (supra), so that a fluid channel is able torelease the color change indicators according to the invention moreeasily.

In another embodiment, the microneedle array is part of a microneedlesystem. Such a microneedle system can be configured with customaryfunctional objects that allow fixation on the skin as well as easyhandling for exerting pressure onto the skin, in particular at least onereservoir and one applicator.

The microneedle system can comprise at least one reservoir, whichcontains at least one arbitrary substance, and in particular an activeingredient, an auxiliary agent or a medicinal drug, preferably in theform of a solution or preparation.

The reservoir is used to store the at least one arbitrary substance,active ingredient or medicinal drug included in the system.

The reservoir is connected to the passages of the hollow microneedles insuch a way that a liquid connection exists between the reservoir and thepassages of the microneedles connected to the reservoir. In this way,the content of the reservoir can be released from the reservoir via thepassages of the microneedles out of the microneedle system when pressureis exerted onto the reservoir after the microneedle system has beenapplied to the skin. The preparation on hand exits the microneedlesystem at or in the vicinity of the tips of the microneedles and canpenetrate into the target tissue. The reservoir is usually attached to asurface of the planar carrier, this being the surface of the carrierlocated opposite the surface of the carrier from which the microneedlesproject.

The reservoir is easy to compress so as to offer little resistance tothe pressure exerted onto the reservoir, and thereby be able to pass thepressure on to the preparation contained in the reservoir for the sameto exit. According to one embodiment, the reservoir can be present inthe form of a flexible bag, for example.

According to a preferred embodiment, the reservoir is designed as a pador a balloon and produced from elastic material, for example from anelastomeric polymer or rubber. Examples of polymers include polyesters,such as polyethylene terephthalates (PET), polycarbonates (PC),polyether ketones (PAEK), polyethylene naphthalate (PEN), polybutyleneterephthalates (PBT), the polyurethanes (PU), polystyrenes (PS),polyamides (PA), polyoxymethylene (POM), polyolefins such aspolyethylene (PE) and polypropylene (PP), polytetrafluoroethylene(PTFE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC),polylactate (PLA) and cellulose-based plastic materials, such ascellulose hydrate or cellulose acetate.

In another preferred embodiment, the microneedle system comprising amicroneedle array is configured with an applicator. Such applicatorsadvantageously allow a pressure mechanism to be activated for themicroneedle array to penetrate the skin or stratum corneum (see, forexample, WO2008091602A2, WO2016162449A1).

According to a further embodiment, the microneedle array can comprisefixation means that are preferably attached to the skin of a patient ortest subject by way of a contact adhesive strip or patch. Suitablecontact adhesives include high viscosity substances that adhere to theskin after briefly applying minor pressure, known as pressure-sensitiveadhesives (PSA). These have high cohesion and adhesion forces. It ispossible, for example, to use poly(meth)acrylate-based,polyisobutylene-based or silicone-based contact adhesives.

The invention thus relates to a microneedle array according to theinvention for intradermal delivery, which comprises fixation means forthe skin.

According to the invention, the term “intradermal delivery” (synonym:“intracutaneous delivery”) describes the administration of arbitrarysubstances via the microneedle array into the skin and requires themicroneedles to pierce the skin.

The invention thus likewise relates to a method for intradermaldelivery, wherein at least one substance is delivered by means of amicroneedle array comprising fixation means for the skin and a pluralityof microneedles on a carrier, wherein the microneedles and/or thecarrier include a pH indicator.

The following examples are provided to further describe the invention,without limiting the invention to these examples.

EXAMPLE 1: VERIFICATION OF FUNCTIONALITY

Use of nitrazine yellow (pH indicator) for the delivery by means ofmicroneedles. After successful delivery, a blue coloration is visible tothe naked eye after approximately 10 seconds. The different pH value onthe skin surface of pH 4 to 5.5 compared to the pH value of the stratumcorneum of pH 6.5 to 7 allows a differentiated assessment of thepenetration.

a) blue coloration indicates a successful delivery, that is, penetrationof the microneedles into the stratum corneum;

b) the skin remains unchanged or takes on a slightly yellowish tint,that is, no successful penetration of the microneedles into the stratumcorneum.

In this exemplary embodiment, minute amounts of nitrazine yellow (0.02%)were added as the indicator into the matrix of the microneedles.

EXAMPLE 2

Another exemplary embodiment is the use of color change indicators,which takes advantage of the presence of a substance available in theskin that, in contrast, is not present on the outer layer (epidermis).

Such a color change indicator can be made of one or more substancecomponents. The presence and absence of a substance in the skin are tobe understood to represent relative information and, with respect to asuccessful penetration into the skin, have to reach a distinguishingfeature sufficient for the indicator.

Within the meaning of the invention, the use of a glucose-sensitiveindicator is, in particular, an obvious choice, without being limitedthereto. For this purpose, the reaction known for the detection ofglucose in human bodily fluids can be utilized, in which the oxidationof glucose by glucose oxidase, and a subsequent reaction of the reactionproducts catalyzed by peroxidase, result in the color change of asubstance subcomponent of the indicator.

Suitable substances for the differentiated assessment of a color changewhen the skin has been penetrated are preferably, but not exclusively,3,3′,5,5′-tetramethylbenzidine (TMB/TMBH2) and derivatives derived fromthe structural class of the benzidines, as well as phthalazines, such as5-amino-2,3-dihydrophthalazine-1,4-dione, and derivatives derivedtherefrom.

When using the leuco form of TMB or TMBH2 as the subcomponent of theindicator, the differentiated assessment of the penetration isaccordingly made possible by the following:

-   -   a) blue coloration indicates a successful delivery, that is,        penetration of the microneedles into the stratum corneum; The        change in color from TMBH2 (colorless) to TMB (blue) is based on        the above-described reaction of the indicator.    -   b) The skin remaining unchanged means no successful penetration        of the microneedles into the stratum corneum and corresponding        absence of the reaction of the indicator substances.

1-16. (canceled)
 17. A microneedle array for use with intradermaldelivery, comprising a plurality of microneedles on a carrier, whereinthe microneedles comprise at least one color change indicator, themicroneedles comprising at least one active ingredient and themicroneedles comprising at least one polymer made of biodegradablepolymers, biocompatible polymers or water-soluble polymers, a colorchange or color shift indicating a sufficient penetration depth into thestratum corneum, wherein the color change indicator is an integral partof the microneedles, the at least one color change indicator beingintroduced or incorporated into the microneedles.
 18. The microneedlearray for use according to claim 17, wherein the color change indicatoris added during the production of the microneedles.
 19. The microneedlearray for use according to claim 17, wherein the microneedles compriseat least one active ingredient.
 20. The microneedle array for useaccording to claim 17, wherein the color change indicator is at leastone pH indicator.
 21. The microneedle array for use according to claim20, wherein the color change indicator is at least one physiologicallyacceptable pH.
 22. The microneedle array according to claim 17, whereinthe color change indicator is a compound selected from chromoionophoresor fluoroionophores, the compound being composed of at least oneionophore covalently bound to at least one molecule, which is selectedfrom chromophores and fluorophores.
 23. The microneedle array for useaccording to claim 22, wherein the chromophores or fluorophores areselected from the neutral, acidic or basic nitrated benzene dyes,neutral, acidic or basic azo dyes, quinone dyes.
 24. The microneedlearray according to claim 17, wherein the color change indicator is ink.25. The microneedle array according to claim 17, wherein the colorchange indicator detects endogenous enzymes.
 26. The microneedle arrayfor use according to claim 17, wherein the color change indicator isincluded in the tip of the microneedles.
 27. The microneedle array foruse according to claim 17, wherein patterns are visible on the skin tothe naked eye.
 28. The microneedle array for use according to claim 17,wherein microneedles made of biodegradable polymers, biocompatiblepolymers or water-soluble polymers.
 29. The microneedle array for useaccording to claim 17, wherein the microneedle array comprises fixationmeans.
 30. The microneedle array for use according to claim 17, whereinthe microneedle array is accommodated in a microneedle system andcomprises at least one reservoir and/or applicator.
 31. The microneedlearray for use according to claim 18, wherein the microneedles comprise amedicinal drug.
 32. The microneedle array for use according to claim 18,wherein the color change indicator is at least one pH indicator, whichis selected from the group consisting of nitrazine yellow, bromothymolblue, carminic acid, brazilin, Congo red, neutral red, phenolphthalein,phenolic red, tetrabromophenolphthalein and a mixture thereof.
 33. Themicroneedle array for use according to claim 20, wherein the colorchange indicator is nitrazine yellow or bromothymol blue.
 34. Themicroneedle array for use according to claim 22, wherein thechromophores or fluorophores are neutral, acidic or basic methines,azomethines, triarylmethane dyes, indoamine dyes, natural dyes, ordirect dyes thereof.
 35. The microneedle array according to claim 17,wherein the color change indicator is biosensing ink.
 36. Themicroneedle array according to claim 17, wherein the color changeindicator detects peroxidases, which do not form part of the epidermis,by means of benzidines or phthalazines.